On Tue, Aug 5, 2025 at 9:28 AM Tao Chen <[email protected]> wrote: > > bpf program should run under migration disabled, kprobe_multi_link_prog_run > called all the way from graph tracer, which disables preemption in > function_graph_enter_regs, as Jiri and Yonghong suggested, there is no > need to use migrate_disable. As a result, some overhead maybe will be > reduced. > > Fixes: 0dcac2725406 ("bpf: Add multi kprobe link") > Acked-by: Yonghong Song <[email protected]> > Acked-by: Jiri Olsa <[email protected]> > Signed-off-by: Tao Chen <[email protected]> > --- > kernel/trace/bpf_trace.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > Change list: > v1 -> v2: > - s/called the way/called all the way/.(Jiri) > v1: > https://lore.kernel.org/bpf/[email protected] > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 3ae52978cae..5701791e3cb 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2734,14 +2734,19 @@ kprobe_multi_link_prog_run(struct > bpf_kprobe_multi_link *link,
even though bpf_prog_run() eventually calls cant_migrate(), we should add it before that __this_cpu_inc_return() call as well, because that one is relying on that non-migration independently from bpf_prog_run() > goto out; > } > > - migrate_disable(); > + /* > + * bpf program should run under migration disabled, > kprobe_multi_link_prog_run > + * called all the way from graph tracer, which disables preemption in > + * function_graph_enter_regs, so there is no need to use > migrate_disable. > + * Accessing the above percpu data bpf_prog_active is also safe for > the same > + * reason. > + */ let's shorten this a bit to something like: /* graph tracer framework ensures we won't migrate */ cant_migrate(); all the other stuff in the comment can become outdated way too easily and/or is sort of general BPF implementation knowledge pw-bot: cr > rcu_read_lock(); > regs = ftrace_partial_regs(fregs, bpf_kprobe_multi_pt_regs_ptr()); > old_run_ctx = bpf_set_run_ctx(&run_ctx.session_ctx.run_ctx); > err = bpf_prog_run(link->link.prog, regs); > bpf_reset_run_ctx(old_run_ctx); > rcu_read_unlock(); > - migrate_enable(); > > out: > __this_cpu_dec(bpf_prog_active); > -- > 2.48.1 >
